Optical switching, multiplexing, and demultiplexing has been accomplished in the past by using an interconnection apparatus having a number of closely spaced input waveguides communicating with the input of a star coupler. The output of the star coupler communicates with an optical grating having a series of optical waveguides, each of these waveguides differing in length with respect to its nearest neighbor by a predetermined fixed amount. The grating is further connected to the input of a second star coupler, the outputs of which form the outputs of the switching, multiplexing, and demultiplexing apparatus.
An example of such an interconnection apparatus is disclosed in U.S. Pat. Nos. 5,002,350 and 5,136,671. The geometry of such an apparatus may be such that a number of separate and distinct wavelengths each launched into a separate and distinct input port of the apparatus will all combine and appear on a predetermined one of the output ports. In this manner, the apparatus performs a multiplexing flnction and may advantageously also perform a demultiplexing function. In this demultiplexing situation, a plurality of input wavelengths is directed to a predetermined one of the input ports of the apparatus. Each of the input wavelengths is separated from the others and directed to a predetermined one of the output ports of the apparatus. Advantageously, an appropriate selection of input wavelength permits switching between any selected input port to any selected output port. Accordingly, these devices are referred to as frequency routing devices and alternative approaches to their design is desired.